Find the magnetic permeability of the iron bar.

1. The problem statement, all variables and given/known data
In a solenoid with 12 enamels for cm passes the current 2 A. Find the magnetic permeability of the iron bar inside it.(B0=1.508 T)

2. Relevant equations
B=μ0*I*N/l(length)

3. The attempt at a solution
We have N/l(length)=1200 enamels/meter
B=4*10^-7*3.14*25*1200=0.003T
Now μr(relative permeability)(if this is what the problem is asking is B/B0=1/500, but in my book it is 500. Where is the error?